Study On The Dynamic Characteristics Of Saturated Tailing Sand Under The Action Of Cyclic Spherical Stress And Cyclic Deviator Stress

With the development of China economy,a large number of discarded tailings will be produced every year in the production process in the chemical and metallurgical fields,and most of the tailings have not been effectively treated,and they are accumulated in the tailings pond by upstream damming technology.In addition,the drainage system of most tailings dams is not perfect,causing most tailings ponds to be saturated.Many tailing dams are also located in high-intensity areas,and the risks of liquefaction,cracks,and settlement of the tailing ponds caused by earthquakes are very great.At the same time,due to the advancement of beneficiation technology and the increase in demand for ore from industrial development,the tailings dams in our country are gradually developing in the direction of fine-grained high-pile tailings dams.Therefore,studying the dynamic characteristics of saturated tailings under seismic loads has high social significance and scientific value.Cyclic triaxial test is one of the effective methods to simulate earthquake load in laboratory.The cyclic triaxial test can determine various dynamic parameters of the soil and provide a theoretical reference for the seismic design of structures.This article analyzes the theoretical principles of unidirectional and bidirectional cyclic triaxial test loading,and compares the advantages and disadvantages of unidirectional and bidirectional cyclic loading and the scope of application;Based on the three-axis symmetric space,the expressions of mean principal stress p and generalized deviator stress q are derived through tensor analysis;it systematically summarizes the setting principles of the consolidation state,phase difference,cycle amplitude,frequency,vibration waveform and other parameters in the cyclic triaxial test.The source of the error that affects the experiment is analyzed,and a solution to reduce the error is proposed.This study can provide a certain reference for the simulation of seismic load in the indoor cyclic triaxial test.In order to explore the influence of seismic loads on the dynamic characteristics of saturated tailings sand,a series of dynamic triaxial tests of cyclic spherical stress and cyclic deviatoric stress was carried out to explore the influence of seismic loads on the dynamic properties of saturated tailings sand simulate the complex stress conditions caused by seismic loads.The test results show that: Under pure cyclic spherical stress,the accumulated pore pressure generated by saturated tailing sand is not enough to cause damage to the sample;Compared with pure cyclic deviatoric stress,the coupling of cyclic spherical-deviatoric stress can inhibit the development of cumulative pore pressure and cumulative plastic strain.Meanwhile,through the analysis of the test results,an empirical growth model of pore pressure coupling for saturated tailings under high-stress conditions is established.And the coupling mechanism of cyclic spherical-deviatoric stress is revealed from the effective stress path、particle breakage and plastic strain mechanism.In order to understand the influence of different loading frequencies and phase differences on the deformation characteristics of saturated tailings sand,a series of dynamic triaxial tests with different loading frequencies and phase differences were carried out for deep-buried saturated tailings sand.The influence of different loading frequencies and phase differences on the dynamic characteristics of saturated tailing sand was systematically studied,and the influence of loading frequency and phase difference on the deformation characteristics of saturated tailing sand was analyzed based on the morphological characteristics of the hysteresis curve(overall tilt degree k,width degree α,area S,unclosed degree ε).The test results show that: Deformation shows reverse "L" type failure,there is a turning point of accumulated plastic strain,and the pore pressure shows a significant increase in stages;Under the influence of different loading frequencies,with the increase of cyclic vibration times,k and α gradually decrease,while S and ε gradually increase.Under the influence of different phase differences,with the increase of cyclic vibrations,k gradually decreases,andα,S,and ε gradually increase.This degree varies with phase difference and loading frequency.A series of cyclic triaxial tests with different consolidation confining pressures and different stress paths were carried out in order to explore the influence of the dynamic characteristics of saturated tailings under the influence of different stress paths.The development law of instantaneous pore pressure and instantaneous strain and the change law of effective stress path are systematically studied.The test results show that under the action of pure cyclic confining pressure,the accumulated pore pressure and residual strain will be generated,while the consolidation confining pressure will affect the change degree of the instantaneous pore pressure and instantaneous strain.With the increase of consolidation confining pressure,the characteristics of periodic fluctuation of instantaneous pore pressure and instantaneous strain are more pronounced.The development of the instantaneous pore pressure will affect the change of the effective stress path,and the inclination and density of the effective stress path will vary with the stress path and the consolidation confining pressure state.In terms of microstructure,under high consolidation confining pressure,the pores of saturated tailings sand body are mainly micropores and small pores.For soil pore distribution,the influence of CSR change is greater than that of RPD change,and the change of effective stress path has a certain relationship with pore change and particle breakage.